Some species, including hammerhead sharks, Komodo dragons, and whiptail lizards, manage to reproduce without males. But not humans. According to new research, that's unlikely to change anytime soon.

The male-specific region of the Y chromosome has just three percent of the genes it had when it began to evolve separately from the X chromosome some 200 to 300 million years ago. Some thought this degeneration might continue, leaving women to sort out reproduction on their own.

"Three hundred million years ago the Y chromosome had about 1,400 genes on it, and now it's only got 45 left, so at this rate we're going to run out of genes on the Y chromosome in about five million years," Professor Jennifer Graves of the Australian National Universitytold The Telegraph in 2009.

This thinking was based on studies of chimpanzees, the closest living relative to humans. But chimp studies were limiting because chimps and humans went their separate ways only 4 million to 6 million years ago, not long in evolutionary terms.

In a study published online in the journal Nature, researchers at the Whitehead Institute in Cambridge, Mass., sequenced the genome of the rhesus macaque, a monkey that split from human ancestors about 25 million years ago.

In doing so the scientists found that the Y chromosome is unlikely to degrade much further. The gene loss that has occurred within the Y chromosome happened rapidly early on, but not much has happened recently. Most of the changes stopped 25 million years ago, they found.

Scientists suggest that nature has stopped selecting for further degraded Y chromosomes.